Cylindrical objects such as roller bearings are commonly inspected for flaws by using eddy current probes. An eddy current probe generates a time-varying electromagnetic field within the metal of the bearing. If the shape of the metal changes, as when the electromagnetic field encounters a crack, the magnetic coupling between the eddy current probe and the bearing is altered. This alteration is detectable and indicates the presence of the crack.
In the case of high-performance roller bearings, such as bearings used in gas turbine aircraft engines, it is desirable to inspect 100% of the surfaces of such bearings, rather than to inspect only sample regions of the surfaces, as is sometimes done.